Method for manufacturing thin-film structure

ABSTRACT

An object of the present invention is to provide a manufacturing method of a thin-film structural body, capable of preparing a thin-film structural body by using a sacrifice film without any protruding part on its surface, thereby preparing a thin-film structural body having high strength and reliability.  
     In order to achieve the above-mentioned object, after a sacrifice film is formed with a film thickness greater than a predetermined value, the surface of the sacrifice film is ground so that the surface of the sacrifice film is flattened with the film thickness of the sacrifice film being adjusted to the predetermined value. Thus, the influence of the surface irregularity of a substrate ( 1 ) is eliminated and the surface of the sacrifice film is flattened. Thereby, a mass body ( 3 ), beams ( 7 ) and fixed electrodes ( 5 ) of a semiconductor acceleration sensor are prepared by using the sacrifice film.

TECHNICAL FIELD

[0001] The present invention relates to a manufacturing method of athin-film structural body formed by using a semiconductor processingtechnique.

BACKGROUND ART

[0002]FIG. 13 is a cross-sectional view showing a thin-film structuralbody formed by using a conventional manufacturing method of a thin-filmstructural body. As shown in FIG. 13, this thin-film structural body101, which is provided with a supporting part 103 and a floating part105 supported by the supporting part 103, is formed above a substrate107 by using a conductive material. The floating part 105 is placed witha predetermined distance from the substrate 107, and sticks out outwardfrom an upper portion of the supporting part 103.

[0003] The substrate 107 is provided with a substrate main body 111, afirst insulating film 113 formed on the substrate main body 111, awiring 115 selectively formed on the insulating film 113, and a secondinsulating film 117 selectively covering a surface of the wiring 115 andthe insulating film 113.

[0004] The surface of the insulating film 113 is flat, and the wiring115 is formed on the surface to protrude therefrom. The supporting part103 is formed on the wiring 115 in a manner so as to cover one portionof the wiring 115. A hole 117 a is formed in the corresponding portionof the insulating film 117 on which the supporting part 103 is to beformed so that the supporting part 103 is connected to the wiring 115through the hole 117 a. The film thickness of the insulating film 117 ismade thin to such an extent that a step difference that is caused on thesurface of the substrate 107 by the influence of the circumferentialedge of the insulating film 117 becomes substantially ignorable.

[0005] In the conventional manufacturing method of a thin-filmstructural body, first, a sacrifice film 121 is formed on the substrate107 having such a configuration as shown in FIG. 14. Next, a portion ofthe sacrifice film 121 at which the supporting part 103 is to be formedis partially removed so that, as shown in FIG. 15, an anchor hole part121 a is formed.

[0006] Successively, a thin-film layer 123 is deposited on the surfaceof the sacrifice film 121 and the surface of the substrate 107 exposedthrough the anchor hole part 121a by using a conductive material, asshown in FIG. 16.

[0007] Next, the thin-film layer 123 is selectively removed andpatterned so that residual portions of the thin-film layer 123 form athin-film structural body 101. In this case, a portion which has beenfitted into anchor hole part 121 a of the residual portion forms thesupporting part 103, and another portion located on the sacrifice film121 forms the floating part 105. Then, the sacrifice film 121 is removedso that a structure shown in FIG. 13 is obtained.

[0008] In such a conventional manufacturing method, in a state shown inFIG. 14, a protruding part 122 a is formed on the surface 122 of thesacrifice film 121 due to the wiring 115 of the substrate 107. When sucha sacrifice film 121 having the protruding part 122 a is used forpreparing the thin-film structural body 101, the following problems areraised.

[0009] The protruding part 122 a has a slanting portion H which islocated above the outer edge of the wiring 115 and which approaches thesubstrate 107 in a direction toward the outside of the wiring 115. Withrespect to the thickness of the supporting part 103, there is alimitation in that if it is too thick, reduction of space is notavailable, and in that if it is too thin, there might be a failure inthe electrical connection between the thin-film structural body 101 andthe wiring 115. Moreover, with respect to the width of the wiring 115,it needs to be thinner in order to save space, depending on its layoutpositions and purposes of use. For this reason, in the case of the widthof the wiring 115 which is made thinner, the supporting part 103 isformed on the wiring 115 with a thickness that is almost the same as thewidth of the wiring 115 as shown in FIG. 13. In a corresponding manner,the anchor hole part 121 a is also formed on the wiring 115 with anopening width which is almost the same as the width of the wiring 115.As a result, as shown in FIG. 15, at least one portion of the slantingportion H remains on the peripheral portion 121 b of the anchor holepart 121 a of the sacrifice film 121.

[0010] The surface shape of this peripheral portion 121 b is reflectedto the shape of the thin-film structural body 101 so that a neck portion131 is formed at a portion corresponding to the peripheral portion 121of the thin-film structural body 101, more specifically, a couplingportion between the supporting part 103 and the floating part 105, asshown in FIG. 13. For this reason, the thin-film structural body 101might be damaged at the neck portion 131 by an impact or the like,resulting in degradation in the strength and reliability of thethin-film structural body 101.

DISCLOSURE OF THE INVENTION

[0011] The present invention has been devised to solve theabove-mentioned problems, and an object thereof is to provide amanufacturing method of a thin-film structural body, capable ofpreparing a thin-film structural body by using a sacrifice film withoutany protrusion on its surface, thereby preparing a thin-film structuralbody having high strength and reliability.

[0012] According to a first aspect of a manufacturing method of athin-film structural body in accordance with the present invention, inthe manufacturing method of a thin-film structural body including: asupporting part (23 b, 25 a) formed on a substrate (1); and a floatingpart (21, 23 a, 25 b, 25 c) integrally formed with the supporting part,supported by the supporting part and placed with a predetermineddistance from the substrate, the manufacturing method includes the stepsof: forming a sacrifice film (51) on the substrate with a film thicknessgreater than a predetermined value corresponding to the predetermineddistance; flattening a surface of the sacrifice film; forming an anchorhole part (51 a) by selectively removing a portion of the sacrifice filmon which the supporting part is to be formed; depositing a thin-filmlayer (53) on the sacrifice film and the substrate exposed through theanchor hole part; selectively removing and patterning the thin-filmlayer so that a residual portion of the thin-film layer is allowed toform the thin-film structural body (21, 23, 25); and removing thesacrifice film.

[0013] According to this aspect, after a sacrifice film is formed with afilm thickness greater than a predetermined value, the surface of thesacrifice film is flattened; therefore, the flattening process of thesurface of the sacrifice film can be carried out without being adverselyaffected by the irregularity on the surface of the substrate.Consequently, since the thin-film structural body can be prepared byusing the sacrifice film having a flat surface, it is possible toprevent an undesired nick portion from being formed in the thin-filmstructural body due to the irregularity of the surface of the sacrificefilm, and consequently to improve the strength and reliability of thethin-film structural body.

[0014] According to a second aspect of the manufacturing method of athin-film structural body in accordance with the present invention, inthe step of flattening the surface of the sacrifice film, the surface ofthe sacrifice film is ground.

[0015] According to a third aspect of the manufacturing method of athin-film structural body in accordance with the present invention, inthe step of flattening the surface of the sacrifice film, the filmthickness of the sacrifice film is adjusted to a value which is equal tothe predetermined value.

[0016] According to a fourth aspect of the manufacturing method of athin-film structural body in accordance with the present invention, inthe step of depositing the thin-film layer, the thin-film layer isdeposited with a film thickness greater than the film thickness of thesacrifice film which has been flattened.

[0017] According to this aspect, since the film thickness of thethin-film layer is set to be greater than the film thickness of thesacrifice film which has been flattened so that the inside of the anchorhole part is completely filled with the thin-film layer. With thisarrangement, it is possible to prevent the edge of an opening of theanchor hole part of the sacrifice film from causing a reduction in thethickness of the portion of the thin-film structural body correspondingto the edge, and resulting in degradation in the strength.

[0018] According to a fifth aspect of the manufacturing method of athin-film structural body in accordance with the present invention, thesubstrate includes a wiring (41, 43, 45) formed in a manner so as toprotrude from the surface of the substrate, the supporting part and thefloating part are made from a conductive material, and the supportingpart is formed on the wiring so as to be electrically connected to thewiring.

[0019] According to this aspect, it is possible to flatten the surfaceof the sacrifice film by eliminating adverse effects from the wiring onthe substrate, and consequently to prevent a neck portion from beingformed in the coupling portion between the supporting part and thefloating part of the thin-film structural body, which has raised aproblem in the above-mentioned conventional technique.

[0020] According to a sixth aspect of a manufacturing method of athin-film structural body in accordance with the present invention, inthe manufacturing method of a thin-film structural body including: aconductive supporting part (23 b, 25 a) formed on a wiring (41, 43, 45)formed on a surface of a substrate (1); and a conductive floating part(21, 23 a, 25 b, 25 c) supported by the supporting part and placed witha predetermined distance from the substrate, the manufacturing methodincludes the steps of: forming a groove (33 a) having a depth of notless than the film thickness of the wiring on the surface of thesubstrate corresponding to at least a portion of the wiring placed belowthe supporting part; forming the wiring on the surface of the substrateon which the groove has been formed; forming a sacrifice film (51)covering the surface of the wiring and the surface of the substrate;forming an anchor hole part (51 a) by selectively removing a portion ofthe sacrifice film on which the supporting part is to be formed;depositing a thin-film layer (53) by using a conductive material on thesacrifice film and the substrate exposed through the anchor hole part;selectively removing and patterning the thin-film layer so that residualportions of the thin-film layer are allowed to form the thin-filmstructural body (21, 23, 25); and removing the sacrifice film.

[0021] According to this aspect, at least a portion of the wiring onwhich the supporting part is to be provided is embedded in the groovehaving a depth of not less than the film thickness of the wiringprovided on the surface of the substrate; therefore, it is possible toprevent a protruding part being formed on the surface of the substrateat the portion on which the supporting part is to be provided.Consequently, it becomes possible to form a sacrifice film having asurface without any protruding part at a portion on which the supportingpart is to be provided without the necessity of carrying out a complexprocess on the sacrifice film, e.g., a flattening process. Moreover, theapplication of this sacrifice film for preparing a thin-film structuralbody makes it possible to prevent a neck portion from being formed atthe coupling section between the supporting part and the floating partof the thin-film structural body, which has raised a problem in theconventional technique, and consequently to improve the strength andreliability in the thin-film structural body.

[0022] According to a seventh aspect of the manufacturing method of athin-film structural body in accordance with the present invention, inthe step of depositing the thin-film layer, the thin-film layer isdeposited with a film thickness greater than the film thickness of thesacrifice film.

[0023] According to this aspect, since the film thickness of thethin-film layer is set to be greater than the film thickness of thesacrifice film, the inside of the anchor hole part is completely filledwith the thin-film layer. With this arrangement, it is possible toprevent the edge of an opening of the anchor hole part of the sacrificefilm from causing a reduction in the thickness of the portion of thethin-film structural body corresponding to the edge, and resulting indegradation in the strength.

[0024] According to an eighth aspect of the manufacturing method of athin-film structural body in accordance with the present invention, thedepth of the groove is set to be equal to the film thickness of thewiring.

[0025] According to this aspect, since the depth of the groove is set tobe equal to the film thickness of the wiring, it is possible to flattenthe surface of the substrate without the necessity of particularlycarrying out a flattening process on the portion on which the supportingpart is to be provided.

[0026] According to a ninth aspect of the manufacturing method of athin-film structural body in accordance with the present invention, thestep of forming the wiring includes the steps of: depositing aconductive film (55) on the substrate having the groove with the samefilm thickness as the depth of the groove by using the same material asthe wiring; and patterning the conductive film so as to remove a portionof the conductive film other than a portion (55 a) located inside thegroove with a predetermined gap dimension (F) from each of the sideedges of the groove so that the residual portion is allowed to form thewiring.

[0027] According to this aspect, since the portion of the conductivefilm formed on the substrate, located inside the groove with apredetermined gap dimension from each of the side edges of the groove,is left, with the other portion being removed, and the residual portionof the conductive film is allowed to form the wiring so that it ispossible to form the wiring with a uniform film thickness, andconsequently to further flatten the surface of the sacrifice film byflattening the surface of the substrate.

[0028] According to a tenth aspect of the manufacturing method of athin-film structural body in accordance with the present invention, thethin-film structural body forms at least one portion of a sensor part(3) which is installed in an acceleration sensor and which has afunction of detecting acceleration.

[0029] According to this aspect, it is possible to improve endurance ofthe sensor part against an impact which is caused, for example, when theacceleration sensor is dropped, and consequently to improve strength andreliability of the acceleration sensor.

[0030] According to an eleventh aspect of the manufacturing method of athin-film structural body in accordance with the present invention, atleast one portion of a circumferential edge of the supporting part (23b) is placed above an outer edge of the wiring (43, 45), and thefloating part (23 a) sticks out from the one portion of the supportingpart and extends in a direction departing from the outer edge of thewiring.

[0031] These and other objects, features, aspects and advantages of thepresent invention will become more apparent in conjunction with thefollowing detailed and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032]FIG. 1 is a plan view showing a configuration of a main part of asemiconductor acceleration sensor to which a manufacturing method of athin-film structural body according to embodiment 1 of the presentinvention is applied;

[0033]FIG. 2 is a cross-sectional view taken along line A-A of FIG. 1;

[0034] FIGS. 3 to 6 are cross-sectional views showing manufacturingprocesses of the structure shown in FIG. 2.

[0035]FIG. 7 is a cross-sectional view taken along line A-A of FIG. 1,which shows a case where a manufacturing method of a thin-filmstructural body of embodiment 2 of the present invention is applied tothe acceleration sensor shown in FIG. 1;

[0036] FIGS. 8 to 12 are views showing manufacturing processes of astructure shown in FIG. 7;

[0037]FIG. 13 is a cross-sectional view showing a structure of athin-film structural body formed by a conventional manufacturing methodof a thin-film structural body; and

[0038] FIGS. 14 to 16 are cross-sectional views showing manufacturingprocesses of the thin-film structural body shown in FIG. 13.

BEST MODE FOR CARRYING OUT THE INVENTION

[0039] 1. Embodiment 1

[0040] As shown in FIGS. 1 and 2, a semiconductor acceleration sensor towhich a manufacturing method of a thin-film structural body ofembodiment 1 of the present invention is applied is provided with asubstrate 1 serving as a sensor substrate, and a sensor part 3 which isformed on the substrate 1 and which has a function of detectingacceleration.

[0041] As shown in FIG. 1, the sensor part 3 is provided with a massbody 21 functioning as a movable electrode, a plurality of fixedelectrodes 23 and a plurality of beams 25. The mass body 21, the fixedelectrodes 23 and the beams 25, which correspond to a thin-filmstructural body of the present invention, are formed by a conductivematerial, e.g., doped polysilicon which is formed by doping an impurity,e.g., phosphorus in polysilicon.

[0042] The mass body 21, which is placed with a predetermined distance Dfrom the substrate 1, has a plurality of movable electrode portions 21 aextending in a direction C which is perpendicular to direction B ofacceleration to be detected. The beams 25, which are integrally formedwith the mass body 21, has a function of suspending the mass body 21above the substrate 1 movably in direction B with a restoring force.Each of the beams 25 is provided with a supporting part 25 a protrudingfrom the substrate 1, a coupling portion 25 b to the supporting part 25a, and a spring portion 25 c provided between the coupling portion 25 band the end edge of the mass body 21 with respect to direction B. Thisspring portion 25 c is elastically bent and deformed so that thedistance between the coupling portion 25 b and the mass body 21 indirection B is expanded and reduced.

[0043] In such a configuration of the mass body 21 and the beams 25, themass body 21, and the spring portion 25 c and the coupling portion 25 band the beams 25 correspond to the floating part of the thin-filmstructural body according to the present invention.

[0044] The respective fixed electrodes 23 are placed along direction Cwith predetermined distances in direction B between each other.Moreover, each fixed electrode 23 is provided with a fixed electrodeportion 23 b forming a floating part which is placed with apredetermined distance D from the substrate 1, and a supporting part 23b supporting the fixed electrode portion 23 a.

[0045] The fixed electrode portions 23 b of the respective fixedelectrodes 23 and the movable electrode portions 21 a of the mass body21 are alternately placed with distances from each other in direction B,thereby forming a capacitor. Thus, acceleration is detected based uponcapacity changes in the capacitor that are generated due to shifts ofmovable electrode portions 21 a.

[0046] As shown in FIGS. 1 and 2, the substrate 1 is provided with asubstrate main body 31 formed by a semiconductor such as silicon, anoxide film 33 serving as a first insulating film formed on the substratemain body 31, a plurality of wirings 41, 43, 45 selectively formed onthe oxide film 33, and a nitride film 47, which serves as a secondinsulating film, selectively covering the surface of the wirings 41, 43,45 and the surface of the oxide film 33.

[0047] The wiring 41 is provided with an exposed portion 41 a placed onthe substrate 1 in an exposed state at an opposing area which faces themass body 21 of the substrate 1, and a contact portion 41 b placed belowthe supporting part 25 a and electrically connected to the supportingpart 25 a. The wirings 43, 45, which are used for drawing signals fromthe fixed electrodes 23, are connected to the respective fixedelectrodes 23 through the contact portions 43 a, 45 a.

[0048] In a corresponding manner, the nitride film 47 has a windowportion 47 a and holes 47 b and 47 c. The exposed portion 41 a of thewiring 41 is exposed to the substrate 1 through the window portion 47 a,and the contact portion 41 a is electrically connected to the supportingpart 25 a. The contact portions 43 a, 45 a of the wirings 43, 45 areelectrically connected to the fixed electrodes 23 through the holes 47b, 47 c.

[0049] In the semiconductor acceleration sensor having theabove-mentioned arrangement, in the present embodiment, the wirings 41,43, 45 are formed on the flat surface of the oxide film 33 in a mannerso as to protrude therefrom. Moreover, the film thickness of the nitridefilm 47 is made thin to such an extent that a step difference caused onthe surface of the substrate 1 by the influence of its circumferentialedge becomes substantially ignorable. Therefore, the portions of thesurface of the substrate 1 on which the wirings 41, 43, 45 are formedare allowed to protrude upward from the other portions by an amountcorresponding to the film thickness of each of the wirings 41, 43 45.

[0050] Moreover, with respect to the thickness of the supporting part 25a, 23 b, there is a limitation in that if it is too thick, reduction ofspace is not available, and in that if it is too thin, there might be afailure in the electrical connection between the mass body 21 and thewiring 41 through the beams 25 and the electrical connection between thefixed electrodes 23 and the wirings 43, 45. Moreover, with respect tothe width of the wirings 43, 45, it is made thinner in order to savespace. For this reason, the supporting part 23 b of the fixed electrodes23 are formed on the wirings 43, 45 with a thickness that is almost thesame as the width of the wirings 43, 45. As a result, at least oneportion of the circumferential edge of the supporting part 23 b islocated above the outer edges of the wirings 43, 45. Moreover, the fixedelectrode portions 23 a are allowed to stick out from the one portionand extend in a thin rod state in a direction departing from the edge ofthe wirings 43, 45. Here, the mass body 21 and the beams 25 are formedin an area surrounded by the outer edge of the wiring 41.

[0051] In accordance with such a configuration of the semiconductoracceleration sensor 1, in the present embodiment, the mass body 21, thebeams 25 and the fixed electrodes 23 are prepared in the followingmanufacturing method.

[0052] First, as shown in FIG. 3, a sacrifice film 51 is formed on thesubstrate 1. In this case, the film thickness E of the sacrifice film 51is set to a value approximately two times the distance D between thesubstrate 1 and the mass body 21 as well as the fixed electrode portions23 a. The sacrifice film 51 is formed by an oxide film, PSG or BPSG, forexample.

[0053] Successively, an etching back process which grinds the surface ofthe sacrifice film 51 is carried out so that, as shown in FIG. 4, thesurface of the sacrifice film 51 is flattened and the film thickness Eof the sacrifice film 51 is adjusted to a value which is equal to thedistance D.

[0054] Then, portions of the sacrifice film 51, in which the supportingparts 25 a, 23 b are to be formed, are selectively removed to formanchor hole parts 51 a. Thus, a structure shown in FIG. 5 is obtained.At this time, on the bottom of the anchor hole part 51 a, the contactportions 41 b, 43 a, 45 a of the wirings 41, 43, 45 are exposed throughthe window portion 47 a and the holes 47 b, 47 c of the nitride film 47.

[0055] As shown in FIG. 6, a thin-film layer 53 is deposited on theresidual sacrifice film 51 and the substrate 1 exposed through theanchor hole part 51 a by using a conductive material, e.g., dopedpolysilicon. The film thickness of this thin-film layer 53 is set to avalue greater than the film thickness E of the sacrifice film 53 whichhas been flattened. As a result, the inside of the anchor hole part 51 ais completely filled with the thin-film layer 53.

[0056] Successively, the thin-film layer 53 is selectively removed andpatterned so that residual portions of the thin-film layer 53 areallowed to form the mass body 21, the beams 25 and the fixed electrodes23. In this case, portions of the residual portions, which have beenfitted into the inside of the anchor hole part 5 la, are allowed to formthe supporting parts 25 a, 23 b, and portions located on the sacrificefilm 51 are allowed to form the mass body 21, the spring portion 25 c,the coupling portions 25 b and the fixed electrode portions 23 a. Then,the sacrifice film 51 is removed so that a structure shown in FIGS. 1and 2 is obtained.

[0057] As described above, according to the present embodiment, afterthe sacrifice film 51 has been formed with a film thickness E greaterthan a predetermined value, the surface of the sacrifice film 51 isground so that the surface of the sacrifice film 51 is flattened withthe film thickness E of the sacrifice film 51 being adjusted to apredetermined value; thus, it becomes possible to flatten the surface ofthe sacrifice film 51 with the influence of the irregularity of thesurface of the substrate 1 being eliminated. As a result, since the massbody 21, the beams 25 and the fixed electrodes 23 can be prepared byusing the sacrifice film 51 having a flat surface, it is possible toprevent an undesired neck portion being formed on the mass body 21, thebeams 25 and the fixed electrodes 23 due to the irregularity of thesurface of the sacrifice film 51, consequently to improve the strengthand reliability of the sensor part 3.

[0058] In particular, each fixed electrode 23 is formed in a manner soas to bridge the outer edges of the wirings 43 and 45 at the connectingsection between the supporting part 23 b and the fixed electrode portion23 a; therefore, in the case where each fixed electrode 23 is preparedby the conventional manufacturing method, a neck portion is formed inthe connecting section between the fixed electrode portion 23 a and thesupporting part 23 b, causing degradation in the shock resistance of thefixed electrode 23. However, in accordance with the manufacturing methodof the present embodiment, the fixed electrodes 23 are prepared withoutcausing any neck portion, making it possible to improve the shockresistance of the fixed electrodes 23.

[0059] Moreover, since the film thickness of the thin-film layer 53 isset to be greater than the film thickness E of the sacrifice film 51which has been flattened, the inside of the anchor hole part 51 a can befilled with the thin-film layer 53. Therefore, it becomes possible toprevent the edge of an opening of the anchor hole part 51 a of thesacrifice film 51 from causing a reduction in the thickness of theportion of the beams 25 and the fixed electrodes 23 corresponding to theedge, and resulting in degradation in the strength.

[0060] 2. Embodiment 2

[0061] The semiconductor acceleration sensor, which is prepared by usingthe manufacturing method of a thin-film structural body according to thepresent embodiment, is only different from the above-mentionedsemiconductor acceleration sensor shown in FIG. 1 and FIG. 2 in that thewirings 41, 43, 45 are substantially embedded in the surface of thesubstrate 1. Therefore, with respect to the semiconductor accelerationsensor to which the manufacturing method in accordance with the presentembodiment is applied, those constituent parts which are the same asthose of the semiconductor acceleration sensor shown in FIG. 1 and FIG.2 are indicated by the same reference numerals, and the descriptionthereof will not be repeated.

[0062] In the manufacturing method in accordance with the presentembodiment, the wirings 41, 43, 45 are embedded in the surface of thesubstrate 1 so that the surface of the substrate 1 is flattened, and byforming the sacrifice film 51 on the substrate 1, it becomes possible toobtain a sacrifice film 51 having a flat surface without carrying out aspecial treatment, such as an etching back process, thereon. Referringto FIGS. 7 to 12, the following description will be given of thecontents of the embodiment in detail. FIG. 7 shows a state where thesemiconductor acceleration sensor has been completed. It is noted thatFIGS. 7 to 12 only show a portion in which the wiring 43 of the wirings41, 43, 45 is prepared.

[0063] First, an oxide film 33 is formed on a substrate main body 31,and groove 33 a is formed in a portion corresponding to the wirings 41,43, 45 on the surface of the oxide film 33. Thus, a structure shown inFIG. 8 is obtained.

[0064] Successively, a conductive film 55, used for forming the wirings41, 43, 45, is formed on the oxide film 33. Consequently, a structureshown in FIG. 9 is obtained. The material of this conductive film 55 isthe same as the material of the wirings 41, 43, 45, and its filmthickness is set to the same as the depth of the groove 33 a.

[0065] Then, the conductive film 55 is selectively removed and patternedby using a mask pattern which is not shown. A portion except for aportion 55 a of the conductive film 55 located inside the groove 33 awith a predetermined gap dimension F from each of the side edges 33 b ofthe groove 33 a is removed. Consequently, a structure shown in FIG. 10is obtained. The wirings 41, 43, 45 are formed by this residual portion55 a. In this case, the surface of the wirings 41, 43, 45 and thesurface of the oxide film 33 are located on the same plane.

[0066] In this manner, each of the wirings 41, 43, 45 is formed insidethe groove 33 a with a margin corresponding to the gap dimension F fromeach of the side edges 33 b so that it is possible to form wirings 41,43, 45 having a flat surface with a uniform film thickness. The value ofthe gap dimension F is set to not more than 0.5 μm, e.g., 0.3 μm. Inthis case, a gap 57 corresponding to the dimension F is provided betweenthe circumferential portion of each of the wirings 41, 43, 45 and eachof the side edges 33 b of the groove 33 a.

[0067] It is noted that, in an attempt to obtain a sufficient effect bypreventing a protruding part from being formed on the surface of thesubstrate 1 due to the influence of each of the wirings 41, 43, 45, thedepth of the groove 33 a may be set to a value greater than the filmthickness of each of the wirings 41, 43, 45. In this case, the surfaceof each of the wirings 41, 43, 45 is located below the surface of theoxide film 33; however, this arrangement makes it possible to prevent aprotruding part from being formed on the surface of the substrate 1 dueto the influence of each of the wirings 41, 43, 45.

[0068] Successively, a nitride film 47 is formed on the entire surfacearea of the substrate 1 in a manner so as to cover the wirings 41, 43,45. Thus, a structure shown in FIG. 11 is obtained. At this time, theinside of the gap 57 is filled with the nitride film 47. Successively,the nitride film 47 is selectively removed by using a mask pattern whichis not shown; thus, a window portion 47 a and holes 47 b, 47 c areformed.

[0069] Here, the film thickness of the nitride film 47 is made thin tosuch an extent that a step difference caused on the surface of thesubstrate 1 by the influence of its circumferential edge becomessubstantially ignorable, and set to a uniform value. Consequently, thesurface of the substrate 1 is set in a substantially flat state.

[0070] Successively, as shown in FIG. 12, a sacrifice film 51 is formedon the substrate 1 formed in this manner with a film thickness G. Thisfilm thickness G is set to a predetermined value corresponding to a gapD. Since the surface of the substrate 1 is substantially flat, thesurface of the sacrifice film is maintained in a flat state without thenecessity of a special treatment, e.g., an etching back process.

[0071] With respect to the succeeding processes, the same processes asthose shown in FIGS. 5 and 6 are carried out; therefore, the descriptionthereof will be given briefly. After the sacrifice film 51 has beenformed as described above, portions of the sacrifice film 51 on whichthe supporting parts 25 a, 23 b are to be formed are selectively removedso that an anchor hole part 51 a is formed. Next, a thin-film layer 53is deposited on the residual sacrifice film 51 and the substrate 1exposed through the anchor hole part 51 a by using a conductivematerial, e.g., doped polysilicon. Successively, the thin-film layer 53is selectively removed and patterned so that residual portions of thethin-film layer 53 are allowed to form the mass body 21, the beams 25and the fixed electrodes 23. In this case, portions of the residualportions, which have been fitted into the inside of the anchor hole part51 a, are allowed to form the supporting parts 25 a, 23 b, and portionslocated on the sacrifice film 51 are allowed to form the mass body 21,the spring portion 25 c, the coupling portions 25 b and the fixedelectrode portions 23 a. Then, the sacrifice film 51 is removed so thata structure shown in FIG. 7 is obtained.

[0072] As described above, in accordance with the present preferredembodiment, the wirings 41, 43, 45 are embedded in the groove 33 ahaving the same depth as the film thickness of the wirings 41, 43, 45provided on the surface of the substrate 1; therefore, it is possible toflatten the surface of the substrate 1, and consequently to form asacrifice film 51 having a flat surface without the necessity of acomplex flattening treatment to be carried out on the sacrifice film 51.Then, the mass body 21, the beams 25 and the fixed electrodes 23 areprepared by using this sacrifice film 51 so that the same effects as theabove-described embodiment 1 are obtained.

[0073] In particular, in the present embodiment, each of the wirings 41,43, 45 is formed with a margin corresponding to a gap dimension F fromeach of the side edges 33 b of the groove 33 a to the inside of thegroove 33 a so that it is possible to form the wirings 41, 43, 45 havinga flat surface with a uniform film thickness. Consequently, even whenthe nitride film 47 is formed with a uniform film thickness, the surfaceof the substrate 1 is flattened more effectively so that the surface ofthe sacrifice film 51 is further flattened.

[0074] While the present invention has been described in detail, theabove description is illustrative in all aspects and the presentinvention is not restricted thereto. It will be understood that numerousvariants which are not illustrated can be supposed without departingfrom the scope of the invention.

1. A manufacturing method of a thin-film structural body including: a supporting part (23 b, 25 a) formed on a substrate (1); and a floating part (21, 23 a, 25 b, 25 c) integrally formed with said supporting part, supported by said supporting part and placed with a predetermined distance from said substrate, said manufacturing method comprising the steps of: forming a sacrifice film (51) on said substrate with a film thickness greater than a predetermined value corresponding to said predetermined distance; flattening a surface of said sacrifice film; forming an anchor hole part (51 a) by selectively removing a portion of said sacrifice film on which said supporting part is to be formed; depositng a thin-film layer (53) on said sacrifice film and said substrate exposed through said anchor hole part; selectively removing and patterning said thin-film layer so that a residual portion of said thin-film layer is allowed to form said thin-film structural body (21, 23, 25); and removing said sacrifice film.
 2. The manufacturing method of a thin-film structural body according to claim 1, wherein in the step of flattening the surface of said sacrifice film, the surface of said sacrifice film is ground.
 3. The manufacturing method of a thin-film structural body according to claim 2, wherein in the step of flattening the surface of said sacrifice film, said film thickness of said sacrifice film is adjusted to a value which is equal to said predetermined value.
 4. The manufacturing method of a thin-film structural body according to claim 3, wherein in the step of depositing said thin-film layer, said thin-film layer is deposited with a film thickness greater than said film thickness of said sacrifice film which has been flattened.
 5. The manufacturing method of a thin-film structural body according to claim 1, wherein said substrate includes a wiring (41, 43, 45) formed in a manner so as to protrude from the surface of said substrate, said supporting part and said floating part are made from a conductive material, and said supporting part is formed on said wiring so as to be electrically connected to said wiring.
 6. A manufacturing method of a thin-film structural body including: a conductive supporting part (23 b, 25 a) formed on a wiring (41, 43, 45) formed on a surface of a substrate (1); and a conductive floating part (21, 23 a, 25 b, 25 c) supported by said supporting part and placed with a predetermined distance from said substrate, said manufacturing method comprising the steps of: forming a groove (33 a) having a depth of not less than the film thickness of said wiring on the surface of said substrate corresponding to at least a portion of said wiring placed below said supporting part; forming said wiring on said surface of said substrate on which said groove has been formed; forming a sacrifice film (51) covering the surface of said wiring and said surface of said substrate; forming an anchor hole part (51 a) by selectively removing a portion of said sacrifice film on which said supporting part is to be formed; depositing a thin-film layer (53) by using a conductive material on said sacrifice film and said substrate exposed through said anchor hole part; selectively removing and patterning said thin-film layer so that residual portions of said thin-film layer are allowed to form said thin-film structural body (21, 23, 25); and removing said sacrifice film.
 7. The manufacturing method of a thin-film structural body according to claim 6, wherein in the step of depositing said thin-film layer, said thin-film layer is deposited with a film thickness greater than said film thickness of said sacrifice film.
 8. The manufacturing method of a thin-film structural body according to claim 7, wherein said depth of said groove is set to be equal to the film thickness of said wiring.
 9. The manufacturing method of a thin-film structural body according to claim 8, wherein said step of forming said wiring includes the steps of: depositing a conductive film (55) on said substrate having said groove with the same film thickness as said depth of said groove by using the same material as said wiring; and patterning said conductive film so as to remove a portion of said conductive film other than a portion (55 a) located inside said groove with a predetermined gap dimension (F) from each of the side edges of said groove so that said residual portion is allowed to form said wiring.
 10. The manufacturing method of a thin-film structural body according to claim 1 or 6, wherein said thin-film structural body forms at least one portion of a sensor part (3) which is installed in an acceleration sensor and which has a function of detecting acceleration.
 11. The manufacturing method of a thin-film structural body according to claim 5 or 9, wherein at least one portion of a circumferential edge of said supporting part (23 b) is placed above an outer edge of said wiring (43, 45), and said floating part (23 a) sticks out from said one portion of said supporting part and extends in a direction departing from the outer edge of said wiring. 